Frost quakes a real possibility, geologist says

SHARON, Pa. (AP) — If you heard a bang or felt the earth shake a bit Tuesday night you weren’t alone.

The noise and accompanying vibration were reported from Hubbard to South Pymatuning Township.

Unlike the mysterious explosion sounds people reported hearing last summer in various parts of Mercer County, this sound was literally closer to home.

“It was like something hit the house,” people said over and over again.

While he can’t say with scientific certainty, geologist Lindell Bridges said he believes the sound came from a phenomenon known as cryoseisms - more commonly known as frost quakes.

“I think it’s a very good possibility,” Bridges said of the clamor and vibrationst. “I think that’s exactly what you heard.”

The president of Pure Earth Resources LLC in Sharpsville is called upon for his services in the oil, gas and mining industries. And while he never experienced a frost quake firsthand, he believes there’s a strong case to be made that such an event occurred in the area.

“It’s pretty uncommon for it to happen — but that doesn’t mean it didn’t happen,” he said.

During past couple weeks frost quakes have been reported in Canada, Wisconsin, Vermont, Cincinnati and elsewhere.

Two primary elements are needed to trigger frost quakes - water saturated ground and a sharp drop in temperature. Both conditions were present; heavy rains last week soaked the ground and in recent days temperatures rapidly dropped more than 40 degrees.

Frost quakes occur mainly at night when temperatures bottom out. As the water in the ground freezes, it expands and cracks the soil, bedrock or stones around it to create room.

“It’s something like an earthquake, Bridges said. “The reason you get an earthquake is stress builds up in the ground and it breaks and releases stored-up energy.”

There are significant differences. Earthquakes occur a mile or two beneath the surface when fault lines shift. Frost quakes are five feet beneath the surface or closer.

“It sounds like the near surface groundwater was frozen and built up some stress and finally exceeded the stress limit and it broke just like an earthquake - only much closer to the surface,” Bridges said.

Besides the sound and vibration, people have reported seeing distant flashing lights before or during frost quakes. Those likely are caused by electrical changes when rocks are compressed. Cracks and fissures may also be seen on the surface, which can range from a few inches up to a couple miles.

Bridges advised anyone who might have experienced a frost quake to check around their homes.

“I would inspect around the house to see if anything is out of order,” he said. “I doubt that it would crack a foundation. But if you have a natural gas or water line and smell or see gas or water seeping, call the gas or water company. Those lines are probably deeper than any damage you might see on the surface - but it’s better to be safe than sorry.”

Mercer County 911 said dispatchers had not received any reports of loud sounds or damage.